This post is about Arduino ProMini WDT issue, causes and fix. I have also included Arduino code to do a quick WDT test on your board.
Please watch the video bellow which demonstrates this issue and explains why you must update your Arduino bootloader if you use WDT in your project.
So to test if your update was successful, you can use my Arduino code. You must connect your Arduino board as shown in diagram bellow. Please note that LCD is optional. You can test it without connecting to LCD and just by observing ProMini onboard LED.
Please download the next file, extract it and upload main code to your Arduino board. Please note that you will need correct LCD library, which I also included in this compressed file.